In November 1942, a stubby, nearly circular airplane lifted off the grass at Bridgeport, Connecticut. It had two three-blade wooden propellers mounted on the wingtips of a wing so short (23 ft span) and so deep (chord almost equal to span) that from below it looked like a flying dinner plate. Charles H. Zimmerman, an NACA engineer who had been working the idea since 1933, called it the V-173. Pilots called it the Flying Pancake. Over the next five years it flew 190 test flights and never crashed — even after one forced landing that flipped it onto its back on a Connecticut beach, from which the pilot walked away and the airframe was flown home a week later.

The physics behind the disc: at a normal wing's tip, a vortex spins off, wasting energy. Zimmerman put a propeller at each tip, rotating opposite the vortex — cancelling it. The result was an aircraft with a theoretical lift-to-drag curve that stayed usable down to almost zero forward speed. The V-173 could fly level at 40 mph and take off in a 20-knot headwind in essentially zero ground roll.

The Navy wanted the combat version. Vought built the XF5U-1: two Pratt & Whitney R-2000-7 radials producing 1,600 hp each, driving 16-foot articulating propellers through cross-shafting so a single-engine failure wouldn't be fatal. Projected performance: 425 mph top speed, 40 mph stall, 20-foot takeoff run. Armament: six .50 cals or four 20mm cannon, plus two 1,000-lb bombs. It would have been a carrier fighter that didn't need a carrier — any 100-foot clearing would do.

Ground runs began in 1947. Taxi tests worked. The propellers, a new all-metal design by Hamilton Standard, developed vibration problems that were being fixed. First flight was scheduled for spring 1947.

Then on March 17, 1947, the Navy cancelled. The reason wasn't the airplane — it was that jet propulsion had arrived, and the Bureau of Aeronautics decided piston-engine fighter development was a dead end. Vought was ordered to destroy the two XF5U-1 airframes. The steel and titanium construction was so tough that wrecking balls bounced off. It took days of repeated impacts to break them up for scrap. The V-173 prototype survived because it had already been transferred to the Smithsonian.

Why now? Every advantage Zimmerman claimed on paper is now vindicated by modern eVTOL research:

• Wingtip-mounted propellers cancel induced drag. Joby Aviation, Archer, and Beta Technologies all use tip-mounted rotors for the same reason. Zimmerman had it in 1933.
• Distributed electric propulsion makes the cross-shafting obsolete. Independent motors driven by a common battery bus solve the single-point-of-failure problem cleanly.
• Composite construction would cut empty weight by ~35%, pushing disc loading into the sweet spot for low-speed lift.
• Fly-by-wire tames the pitch-coupling behavior that made the V-173 exhausting to fly manually.
• The Marine Corps is currently paying billions for F-35B STOVL capability. A disc-wing tiltable-prop utility aircraft could deliver ~80% of the tactical benefit at 10% of the cost per airframe.

The XF5U-1 was not a failed design. It was a finished design killed by a paperwork decision made before it flew, in a program office that had already mentally moved on to jets. The airframes were destroyed so thoroughly that no engineer could resurrect them from parts. What survived is the aerodynamics — and every eVTOL company on earth is now rediscovering, expensively, what Zimmerman proved with plywood and fabric in 1942.